Drill bit



Feb.17,1970 P.w.,scHuMAcHER, JR 3,

. DRILL BIT i Filed July 5, 1968 2 Sheets-Sheet 1 Perry W Jcwzracer;

' l N VENTOR.

ATTOR/VEYJ.

Feb. 17, 1970 P. w. SCHUMACHER, JR

DRILL BIT 2 Sheets-Sheet 2 Filed July 5, 1968 INVENTOR.

United States Patent 3,495,668 DRILL BIT Percy W. Schumacher, Jr., Houston, Tex., assignor to G. W. Murphy Industries, Inc., Houston, Tex., a corporation of Texas Filed July 5, 1968, Ser. No. 742,819 Int. Cl. E21b 9/24 US. Cl. 175-341 10 Claims ABSTRACT OF THE DISCLOSURE A drill bit having skewed roller cutters and a roller cutter therefore having at least one row of hard metal cutting inserts which are suitable for drilling medium formations and which inserts have sufficient strength and present a minimum projected surface area to the varied drag forces exerted on the inserts by the formation during drilling.

SUMMARY The present invention relates generally to an improved drill bit having a skewed roller cutter with hard metal cutting elements or inserts.

An object of the present invention is to provide an improved drill bit for drilling through formations of medium hardness at high penetration rates which has an improved useful drilling life.

Another object is to provide an improved drill bit and roller cutter having an improved rate of penetration in drilling through medium formations.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the improved drill bit and roller cutter of the present invention are hereinafter described and explained with reference to the preferred form of the drill bit of the present invention shown in the drawings wherein:

FIGURE 1 is a perspective view of the improved drill bit of the present invention.

FIGURE 2 is a bottom view of the drill bit illustrating the skewed position of the roller cutters.

FIGURE 3 is a composite sectional view of the roller cutters illustrating the relationship of the placement of the cutting elements or inserts on the roller cutters.

FIGURE 4 is a detail sectional view of the preferred insert used in the roller cutter of the present invention.

FIGURE 5 is a diagrammatic illustration of the drag forces exerted on the inserts during drilling.

FIGURE 6 is a detail sectional view of the protrusion of a modified form of insert used in the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The improved drill bit 10 shown in FIGURE 1 includes a head 12 having a threaded shank 14 for connection to a drill string and three generally frusto-conical roller cutters 16 rotatably mounted to said head by suitable bearings in the bearing extensions 18. The head 12 defines the passageways in which the nozzles 20 are positioned to direct drilling fluid onto the surface being drilled.

As shown in the drawings, the axes 22 of rotation of each of the roller cutters 16 extend inwardly and away from the head 12 and each of these axes is skewed or spaced forward from the longitudinal axis 24 of rotation of the head 12. This skew mounting of the roller cutters 16 introduces a radial drag on portions of the roller cutters during drilling as hereinafter explained with references to the diagrammatic illustration of FIGURE 5.

As shown in FIGURE 3 the roller cutters 16 are rotationally supported on the bearing extensions 18 by the roller bearings 26, the ball bearings 28, the thrust button "ice and the bushing 32. Each of the roller cutters 16 includes at least one row of the hard metal cutting or crushing inserts 34 which are preferably of tungsten carbide. Since FIGURE 3 is a composite view of all three of the roller cutters 16, the inserts 34 are numbered 1, 2 and 3 to designate the roller cutter in which they are positioned and to further illustrate the tracking relationship of the inserts 34 during drilling. Two types of the cutting inserts 34 are illustrated in FIGURE 3. The innermost inserts 34 designated 1 and 2 are shown to have a generally hemispherical protruding shape. The remainder of the cutting members 34 (at least one row on each roller cutter 16) is shown to have a substantially conical shape projection with a rounded or blunted end.

This shape, which is the preferred shape of the protruding or projecting portion of the cutting members or inserts 34, is shown in greater detail in FIGURE 4. The inserts 34 have a cylindrical body 36 with a bevel 38 at one end to facilitate its insertion into the recess 40 defined in the roller cutter 16. The other end of the body 36 which projects beyond the roller cutter 16 defines the conical surface 42 which terminates in the rounded end 44. It is preferred that the included angle of the conical surface be between 45 and 75 degrees. Angles substantially less than 45 have a tendency to wear rapidly and to be subject to excessive breakage. Angles substantially greater than 75 degrees are not believed to have sufficient protrusion to accomplish the improved penetration rates desired. The insert of the present invention has a protrusion of at least one-half of the diameter of its cylindrical portion.

Circumferential drag is caused by the: rotational velocity of the inserts on the outer row of a roller cutter being different than the rotational velocity of the inserts on an inner row of inserts. This velocity difference results from the roller cutters 16 having other than a true rolling contact with the formation being drilled because of the arcuate contour of such contact as best seen from FIG- URE 3. This difference in rotational velocity causes one of the inserts to be dragged or skidded in the formation when an insert in another row of the same cutter firmly engages the formation. This drag on the inserts 34 is a generally circumferential direction as indicated by the arrows 46 and. 48 in FIGURE 5. The skew of the roller cutter 16 produces a radial drag of the inserts 34 as indi- (cated by the arrows 50 which results :in radial forces on the inserts 34. The arrows 46, 48 and 50' illustrates the possible drag of two inserts 34 on a single roller cutter 16 when drilling a well bore as shown schematically in FIG- URE 5. The forces on an insert may thus be the resultant of any combination of the component forces and may vary as the cutter rolls on the formation.

It has been discovered that to have the increased drilling rate which can result from the combination of radial and circumferential drag without sacrificing the life of the drill bit, the sectional area of the projecting portion of the inserts 34 taken in a plane normal to the resultant drag force should be as small as possible while maintaining the strength of the insert to minimize breakage. Since these drag forces vary continually in both direction and amount, it is preferred the section area taken in any plane through the centerline of the insert be substantially conical shape with an included angle between 45 to degrees and a rounded or blunted end. The rate of drilling penetration in medium formation depends on the degree of sharpening of the projecting ends of the cutting elements 34. While the preferred configuration of the cutting elements 34 is the conical shape illustrated, a cutting element may be formed by sharpening on several sides to have a pyramid shape to obtain the desired penetration rate while maintaining a relatively small projected area on which the drag forces are developed. These minimum projected areas of the inserts 34 in which the strength is maintained greatly increase the drilling life of the drill bit by minimizing the loss and breakage of the inserts 34.

As previously mentioned, the ends of the inserts are rounded as shown in FIGURE 4 or blunted as shown at 4411 on insert 34a in FIGURE 6 to avoid the damage to the insert which would result if it terminated in a conical point. Thus, the blunting may be accomplished by forming the insert to have its outer extremity rounded or truncated. Similarly a pyramid shaped insert or an insert having a shape approximating a cone, such as an ogive shape, should be blunted at its outer end.

From the foregoing it can be seen that the drill bit and roller cutter of the present invention provide improved penetration rates in drilling by the utilization of both circumferential and radial drag without a loss of effective drilling life.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

- 1. A drill bit, comprising a head,

at least one roller cutter,

bearing means for rotatably mounting said roller cutter on said head,

the axis of rotation of said cutter extending inwardly and away from said head generally toward and skewed from the axis of rotation of said head,

said cutter having a plurality of hard metal cutting elements inserted therein,

each of said hard metal cutting elements in at least one row having a protrusion of at least one-half of its diameter, sufiicient strength to minimize breakage and a minimum projected area both axially and circumferentially of said cutter.

2. A drill bit according to claim 1, including three of said roller cutters.

3. A drill bit according to claim 1, wherein said roller cutter is generally frusto-conical in shape,

the relationship between the locations of the inserts and the offset of the axis of the roller cutter from the axis of rotation of said head causes some of said cutting elements to drag in both circumferential and radial directions during drilling.

4. A drill bit according to claim 1, wherein said cutting elements have a substantially conical shaped protrusion.

5. A drill bit according to claim 4, wherein the cone angle of said conical shaped protrusions is substantially in the range from 45 to degrees.

6. A drill bit according to claim 4, wherein the outermost portion of each of said conical shaped protrusions is blunted.

7. A roller cutter adapted to be skew mounted on a drill bit, comprising a generally frusto-conical body, and

a plurality of hard metal cutting elements inserted into said body with a portion of each of said elements projecting outwardly from said body,

at least a portion of said cutting elements having a protrusion of at least one-half its diameter, suflicient strength to minimize breakage and a minimum projected area both axially and circumferentially of the axis of said body whereby drag forces developed on said cutting elements is minimized.

8. A roller cutter according to claim 7, wherein the protruding portion of said cutting elements is substantially conical.

9. A roller cutter according to claim 8, wherein the cone angle or said cutting elements is substantially in the range from 45 and 75 degrees.

10. A roller cutter according to claim 8, wherein the outermost portion of each of said conical shaped cutting elements is blunted.

References Cited UNITED STATES PATENTS 2,148,372 2/1939 Garfield -341 3,137,355 6/1964 Schumaker 175-374 3,223,188 12/1965 Coulter et al 175-341 3,388,756 6/1968 Varel et al. 175-410 3,388,757 6/1968 Fittinger 175-410 3,389,761 6/1968 Ott 175-374 3,442,342 5/1969 McElya et al. 175-374 DAVID H. BROWN, Primary Examiner US. Cl. X.R. 175-353, 374, 410 

